The invention relates to a method and arrangement for determining the concentration of nitric oxide gas in an unknown gas mixture. Such methods are important in industry for the testing and assessment of new motors and gas turbines, which produce unknown exhaust gas mixtures. The arrangements are also utilized for determining air pollution levels in cities and other environments which are subject to pollution from exhaust gases, and contain nitric oxide gas concentrations.
Previous known methods of nitric oxide concentration measurement utilize nondispersive infrared spectroscopy (NDIR) or chemiluminescence methods. The nondispersive infrared spectroscopy method is too inaccurate and too insensitive; the chemiluminescence method is not suitable for the measurement of rapid changes in gas concentrations in exhaust gases. The measurement cell must be operated in a partial vacuum (5 to 10 mm Hg) and requires considerable time, and the complete evacuation of gas. This method also requires permanent production of ozone in normal operation; and an automatic operation is not easily practicable or possible. It is also necessary to calibrate the instrument regularly with no gas mixtures of known concentrations and to correct the values for quenching effects.